Concerning the crossing symmetry equations, for spinning fields the factor \(\Omega (x_i)\)  becomes a \(n\times m\)  matrix with \(n = \dim V\)  and \(m=\dim W\) . The ratio of two prefactors that correspond to different permutations \(\sigma \)  is replaced by an \(m\times m\)  matrix \(M\)  whose entries depend on \(x_i\)  only through cross ratios. This crossing factor \(M\)  have been derived in several cases, usually for low spins, in [1]}, [2]}, [3]}, [4]}, [5]}, [6]}.
